If just for Yoda. A big build-up in Empire is Luke expecting to find this wise and silent Jedi master...and he finds a weird old lepprechaun looking muppet. You don't even know how great he is until he uses the force to lift Luke's ship out of the lake.

But that's all spoiled if he's introduced already in Eps. 1-2. In those he starts off as the quiet old Elder (with far less personality). And you see him fighting. By the time you get to Empire, he's no big deal anymore.